The present invention relates to a fuel injector.
A fuel injector which has a valve needle operated by an actuator is already known. The actuator includes, for example, an electromagnetic coil or a piezoelectric element. An example of a fuel injector of this type is described in German Patent 35 40 660 C2. This fuel injector is capable of being actuated electromagnetically. The fuel injector has a valve housing containing a magnetic coil installed on a field spool. The valve needle combines with a valve-seat surface to form a sealing seat. The end of the valve needle facing the magnetic coil is permanently connected to an armature. Armature and valve needle are moved against the sealing seat by a restoring spring. If a voltage is applied to the magnetic coil, and a current subsequently flows through it, the armature is attracted to the force of the restoring spring by the magnetic field created and it lifts the valve needle off its sealing seat. The fuel can now exit through the injection bore downstream from the valve seat.
The disadvantage of this known fuel injector is the fact that the fuel distribution and quantity can only be controlled to a limited extent. The direction in which the fuel exits the fuel injector is determined by the orientation of the injection bore. An adaptation to various operational conditions, such as is necessary in the case of the lean-burn concepts and stratified-charge methods in combination with direct injection into the combustion chamber in particular, is very difficult or not possible at all.
From German Patent 40 23 233 A1 a fuel injector is known, which has, at its combustion-chamber end, two hole circles made up of injection bores. In order to be able to separately control the two hole circles, the fuel injector has two coaxial valve needles in one nozzle body. In the region of the combustion-chamber side end sections of the two valve needles, there is also a separating sleeve installed between the two valve needles, whose end face cooperates with one valve seat surface, common to the valve seat surfaces of the two valve needles. The two hole circles are supplied with fuelxe2x80x94along the valve needlesxe2x80x94by individual fuel intakes, with each of the two fuel intakes having its own fuel injection pump. This makes it possible to configure the flow rate and orientation of the injection bores of the two hole circles differently from one another and, therefore, control the direction and quantity of fuel injection to a certain degree by triggering the two valve needles separately. The disadvantage, however, is the overall multicomponent design, since three high-precision componentsxe2x80x94the two valve needles and the separating sleevexe2x80x94must be manufactured in such a way as to ensure the most precise fit possible, and the fact that it is necessary to provide two fuel injection pumps, or one fuel injection pump doing double duty for each fuel injector. This results in additional costs. Another disadvantage is that there are a total of three sealing seatsxe2x80x94one for the first valve needle, second for the second valve needle, and third for the separating sleeve. Furthermore, it is also disadvantageous that triggering occurs purely hydraulically, and no individual regulation based on a characteristic map is possible to the extent possible, in the case of a fuel injector controlled by an actuator.
From published German Patent Application 27 11 391 A1 a fuel injector is known that has two valve needles. Both valve needles are acted upon in the closing direction by one spring each and cooperate with one valve seat surface each to form a sealing seat. Different injection orifices are opened by the two valve needles. Control of the valve needles is purely hydraulic, with the opening sequence being determined by the varying spring force of the two valve needle closing springs. An adaptation to performance data of an internal combustion enginexe2x80x94as is typically possible with an actuator-controlled fuel injectorxe2x80x94is therefore not feasible.
The fuel injector according to the present invention has the advantage over the related art that a fuel distribution in the combustion chamber is possible, which adapts to the requirements of the characteristics map and especially to a lean-burn concept.
In particular, the angle under which the fuel is distributed in the spray pattern of the fuel injector, is changeable. This is possible with the fuel injector according to the present invention due to the design using two valve needles, each of which is operated by its own actuator. Moreover, actuation via one actuator at a time, makes the fuel injector easily adaptable to a characteristics map of the internal combustion engine.
With this invention it is possible to actuate two different hole circles containing injection bores by the two sealing seats of the two valve needles in an advantageous manner.
The injection bores of the different hole circles may have, in particular, different injection angles and be offset against each other. This is also advantageous since, in the case of a small injection quantity and engine load, it is possible to initially actuate only one valve needle, so that a first hole circle is opened. This invention also has, for example, a narrow injection angle of the injection bores, so that a fuel injector jet, made up of the fuel jets of the individual injection bores, is formed having an overall narrow angle range. At a higher load of the internal combustion engine and corresponding demands, during stratified-charge operation, of an internal combustion engine using the lean-burn concept, the second valve needle is lifted off the sealing seat as well. This now also opens up the second hole circle of injection bores. These bores may have a larger injection angle. Thus with this invention the total spray of fuel injected is supplied in a greater angular range.